As is disclosed in Japanese Utility Model Laid-Open No. H6-48887, in a conventional optical print head, a light-emitting device (array) has a plurality of individual electrodes provided on the front surface of the device so as to correspond one to one to a plurality of light-emitting parts formed on the device, and has a single electrode provided on the back surface of the device so as to be common to all of those light-emitting parts. This makes it impossible to perform time-division driving within a single device. Since it is impossible to perform time-division driving, it is necessary to provide as many individual electrodes as light-emitting parts. Thus, as the light-emitting parts are formed at higher and higher density, the individual electrodes need to be formed at accordingly high density, making their connection to a driving IC difficult.
To solve this problem, Japanese Patent Application Laid-Open No. H6-163980 proposes a light-emitting device that permits time-division driving within the device. Specifically, a plurality of light-emitting parts arranged on the light-emitting device are divided into p, for example 2 or 3, groups, a plurality of common electrodes are provided so that each of them is connected to all the light-emitting parts of one of those groups, and n individual electrodes are provided so that each of them is connected to p light-emitting parts belonging to different groups. Thus, the light-emitting device proposed here is provided with p×n light-emitting parts in total. In this light-emitting device, by selecting one of the p common electrodes on a time-division basis, it is possible to reduce the number of individual electrodes needed to 1/p the number needed conventionally, and thereby make their connection to a driving IC easier.
This light-emitting device can be driven on a time-division basis by using a driving IC as used conventionally. In this case, however, a separate driving circuit is additionally necessary to select one of the common electrodes on a time-division basis. To avoid this, there has been demand for the development of a versatile driving IC suitable for time-division driving.
Under these circumstances, the applicant of the present invention once proposed a driving IC in Japanese Patent Application Laid-Open No. H10-226102, with consideration given to the aforementioned points. However, with the configuration proposed here, it is necessary to change the order of data input to achieve time-division driving, which involves complicated processing of data. Moreover, it is necessary to use as many driving ICs as light-emitting elements used; that is, it is necessary to use many driving ICs at accordingly high cost. Furthermore, this driving IC, when applied to light-emitting devices having different resolutions, requires complicated processing of data.